At present, there is not available on the commercial marketplace an acceptable process and apparatus for erecting corrugated cardboard box flats and gluing the flaps together using a liquid cold adhesive. Such boxes are used as cases for packaging various articles such as cans and the like. The reason for this absence is simple--it takes 4 to 6 seconds using conventional case erecting and gluing systems for a cold adhesive to reach a cure stage that causes the glued components of the box to adhere together to a point where subsequent operations can be done to the case. Most commercial box or case construction lines run at a rate of 20 to 30 boxes per minute and consequently, the 4 to 6 second cure time is not economically viable. The assembly line has to be unduly and uneconomically long in order to provide the 4 to 6 second adhesion time before the box or case can be filled or used.
Cold cure adhesives have also been generally disfavoured because it has been believed that such adhesives cannot be applied to a surface, set and dried, and then subsequently used in adhesive applications by rewetting the dried adhesive. The adhesive strength obtained in such applications has generally been found to be unsatisfactory.
Because of the slow cure time required for liquid cold adhesive systems, the preferred practice in corrugated box or case construction has been to use a hot melt adhesive. Hot melt adhesives have the advantage that they have a relatively rapid adhesive cure time. Unfortunately, however, these adhesives have a number of serious shortcomings.
They generally cost about two times more than cold cure adhesives. Furthermore, the equipment required to spray and apply hot melt adhesives costs about five times the cost of cold cure adhesive application equipment.
A second serious disadvantage is that hot melt adhesives have considerably lower adhesive strength than cold cure adhesives. Hot melt adhesives are relatively viscous and this detracts from the ability of the hot melt adhesive to be spread in a thin discrete particulated pattern which is required to provide a strong adhesive bond. Further, the high viscosity inhibits the hot melt adhesive penetrating the fibres of the corrugated cardboard and forming a strong bond.
A third major disadvantage with hot melt adhesives is that they tend to be brittle at cold temperatures, and hence boxes or cases using hot melt adhesives are not useful in freezer environments or in winter packaging applications.
In view of the foregoing, it can be readily understood that there is a strong need in the marketplace for a rapid cure cold melt adhesive system that can be used for gluing corrugated boxes or cases together from corrugated cardboard blanks.